I saw this wad in an early version a while back when I was lurking around deathmatch servers trying to find random wads to download, I see you added a duel side to it so I will now break your wad down map for map beginning with dm
Spoiler: deathmatch (Open)usdm01: opening map is an arena, don't particularly fancy these. In the center there are 4 powerups to grab, green armor, blue armor, megasphere and berserker, in close proximity too so with a bit of grace and maneuvering an aware player can grab all 4 powerups to deny other players which can potentially lead to some unbalancing. The stairs leading back up to the second floor should be made a bit wider as normal strafe running up breaks momentum twice while ascending. The triggers to activate the lifts on the outside where the shotgun sits is a bit out of the way, perhaps a longer linedef to set it off? Other than that it's alright for an arena, I like the sky and the textures and detail make it look pleasant for the most part.
usdm02: This map already feels a bit clunky, lots of tight corridors and maze like hallways can lead to some confusing gameplay with a simple 4 player deathmatch trying to find other players. Lots of clusters of ammo just lying around the place and with the plasma gun located by a mega armor then there is no real punishment to just running around and holding the fire button. In addition to the ammo clusters there are also plenty of health clusters meaning most encounters will most likely end up as whoever can skate over as many health packs first. My last nitpick for this map would be the only door located in here which has 2 switches located opposite to the door meaning having to turn to activate then turn to run through, to me this is no big deal but to others this could become mildly irritating. Texturing here is also well done as most of the textures compliment and work off eachother.
usdm03: Seems to be another arena style map with the added twist of secret powerup/weapon caches. The secrets are alright, but the plasma gun on this particular map sort of makes it more desirable to just run around the outside area killing fresh spawns. Now at first I was confused by the areas I couldn't get to so I used 'iddt' and explored around and found lots of rooms which seem to have no entrances or just lead to nowhere until I realized the gametype wasn't set to deathmatch. With this on I discovered a harshly glaring issue within these maps and that is your spawn locations. I went back to 1 and 2 and found that you actually put 3 spawns in a row around a single gun meaning 1 of those 3 spawns will be fortunate enough to actually start with a gun. This is a massive deal as players who tend to familiarize themselves with a map need to know what their area looks like when they spawn and what weapon they will need to run to once they gain control, I've yet to play any of these maps on a server and already I'm irritated by this. Especially in a deathmatch environment, pistol spawns can either make or break a map depending on the size and spawn locations. A good example would be map28 from the idl wad which had a pistol spawn that drove players crazy since all other spawns were on weapons. Regardless of this diversion let us continue on. Only left to say about this particular map is the brick texture here, I never really liked it so it's a biased opinion on my end, just looks out of place and ugly especially as a stand alone texture.
usdm04: This map suffers from some of the same issues with too many tight hallways and maze like designs. The actual open parts are interesting and fun however, I wanted to see more of that. My absolute main issue with this map is the fact that getting the plasma gun is harder than getting the bfg here and not only that there is a red armor next to this bfg. The only flip side to this is all the cells are located on the opposite end of the map, getting to it might not be all that easy as I managed to get lost once or twice. However it is a reward for getting to this area as there is 6 big cell packs and plenty of cover to shoot bfg balls at to activate the tracers coupled with the fact there are I think 9 pistol spawns located up the stairs with 0 walls covering them. The 64 px doorways are a real nuisance and honestly makes the grenade launcher really stand out in this map as most hallways turn so much it's difficult to have much reaction time to grenades bouncing towards me. The texturing here is okay, but it does get bland after quite some time and should really move the door triggers back some as I keep running into the doors before they open even if I run straight at them.
usdm05: Another arena map not much to comment here actually. The spawn room before actually spawning is a nice touch, but leaves players completely vulnerable upon exiting especially when teleporting to a fixed 'spawn'. Map looks a lot better than the previous 2 so far though.
usdm06: Well yet another arena set to a certain theme ala dead simple style. Not much to say here other than the insane amount of pistol spawns all around the map, 4 spawns in a row is a bit overdoing it.
usdm07: This one is a lot more pleasing to look at and to run around in -- in some places that is. The two weird things about this map is the random damage pit at the top of some steep stairs and the really really really tight 'library' room I think it is.
usdm08: Compared to the previous maps this is less arena styled and less tight hallway made. Nitpick here, but the amount of small boxes around this map make it awkward when running over 4 or 5 of them with the sudden changes in view. The bfg is located by jumping up to a megasphere which basically guarantees anyone to get it with little to no resistance as the path is pretty high up and unwary players aren't exactly looking at the ceiling at all times. Again the door triggers need to be set back more, waiting for doors in fast pace dm is a bit too slow.
usdm09: I just do not like this map. The spawns are located in some really awkward places so anyone spamming in any of these rooms fresh spawns will just fall down to an incredibly slow damage lava pit. Railgun is the only weapon worth getting here, run into the outer area, then keep distance and snipe anyone coming out the slow doors which there are a lot of with the same issues as before, move those door triggers back.
usdm10: Essentially a spam map with a 'pick your own powerup' motif over it. Every spawn is a rocket launcher spawn and throughout the map are skulltag runes and other various powerups located on top of boxes. Most of these can be obtained by jumping from spawns then from box to box as there is high air movement making the high jump rune kind of null. I have a firm belief that the skulltag runes have no place in deathmatch as they give one player essentially too much power over the others like with the strength or rage runes which are the only 2 one should really get in a map like this and with all the ammo littering the map it's a bit difficult to really get punished for simple running around holding mouse1 (or any other fire button one is accustomed to).
usdm11: Basically hallway connected to hallway all the way around the outside with a massive and confusing maze that no player should really venture into. Again this map has an issue with small boxes protruding out from the ground making the running really awkward in this long stretch of hallways, as well as the hallways should either be made smaller or have some type of break in between as they are truly massive. The maze is really annoying to navigate, I frequently needed to pull up automap to make my way to any teleporter which in an ongoing deathmatch I would not really be favored to do.
usdm12: arena
usdm13: Now this operates and looks more like a standard dm map. The only weird thing about it is the fact that both of the areas that are separated via door are too... Well separated and there needs to be more connectivity between the two as one leads to just a dead end forcing players to have to walk all the way back to get to the action. There are some high jump runes here, I don't see any real need to get one as there are no jumps needed with it.
usdm14: This is getting a bit better now, nice sizeable map with reasonably placed obstacles. Not sure how I feel about all the caution texture, but it is detail nonetheless. And as in the previous map where there was a lack of connectivity there is now way too much connectivity. Plenty of lifts that lead to the same room all located directly next to eachother alongside a door which also leads to the same exact room, either open up more of these paths or make the doors bigger as these tend to get a bit confusing after some time.
usdm15: arena
usdm16: This map includes a megasphere into bfg into timesphere, no absolutely not.
usdm17: Really need to do something about these tight inner rooms, they just deter so much from the action and are simply a pain to move through, especially when some of the bookcases are actually visibly blocking where the exits are. Even though jumping is disabled, freelook is not and I was able to rocket jump to all 4 invulnerability spheres located at the corners of this map, should make those blocks impassable or remove the spheres because that is actually a serious issue to deal with.
usdm18: joke arena
usdm19: dead simple times 4
usdm20: not finished I assume
Spoiler: duel (Open)usdl01: With duels I do plan to be more critical as these types of maps require more thought put into them as they should have. However already we start off with an arena which includes 2 soulspheres and one green armor and then one blue armor. When it comes to duel the lifts need to ascend faster or be put in a spot where players can be given the chance to survive long enough to actually go up. The blue armor vs the green armor really makes a difference on whichever one is grabbed first as the player who gets a soulsphere and blue armor is going to win more so than the player who gets soulsphere and green, especially if the player who grabs blue controls the map to their favor. The spawns here are absolutely unforgivable, all of them are pistol spawns but only 2 actually spawn players on weapons.
usdl02: 4 hallways connected to the center with all the hallways split in half with a curve at each one so technically 8 hallways. This map just comes off as lazy with 0 weapon variation and the chaingun in the center is simply a waste as this map is tight and really has no use here whatsoever. This map does offer all the spawns on weapons however so this is nice.
usdl03: This map is simply too small to really be a viable duel map, the plasma and rocket launcher reign supreme here as all the curves in the hallways make it difficult to play around someone spamming both sides. With mass ammo for the plasma it would be incredibly easy to control all the pistol spawns using just the plasma.
usdl04: Again with the lined up spawns over one gun, this cannot be overlooked in duel ever and they must be removed for just the one spawn. This map also includes a red armor and a haste rune, in combination this already breaks this map's chance at being a duel map with such overpowered items.
usdl05: The over abundance of lifts just to get irritating in this map as it requires way too much effort to put one self into a situation where grabbing the rocket launcher is just a suicidal mission. With how the spawns are set up the only weapon that should be used here is the ssg and nothing else as they all require too much time to grab and when the sounds of lifts can be heard anywhere in this small map there is no chance of getting out of those rooms with the chaingun or plasma.
usdl06: There is no real balance in this map, the rocket launcher is key to winning here as a player can just run to either side of the map and stand at the edge and spam inwards. Going through the doors to try and kill anyone is a nightmare as the triggers here really need to be pulled back some otherwise a run in with a rocket or grenade can be anyone's fate doing so. All spawns are inside anyway, all 6 of them so whoever spawns on an ssg then gets the first kill can then immediately and quite literally stand still and kill their opponent spawn after spawn since they are located right beside eachother.
usdl07: No duel map should include massive damage pits and tall but skinny cliffs surrounding it. Here it's basically get the ssg and stay up top and essentially they will win as all spawns are pistol spawns again and getting around the map takes very little time. And there is an inviso sphere here, this is no longer a duel map. And a megasphere is here as well.
So for the summary, almost all the maps currently represented here are either wildly unbalanced or a pain to play with tight hallways and corridors and some abnormal geometry. I saw this wad prior to this and I don't know what happened since then to now, but the earlier version was much smoother and had more thought put into it and had actually lots of ambition put into it from what I saw previously. This needs serious reworking if it is to look adequate again.
-Loosen up on the arenas
-Add more weapons to the duel maps
-Stick to one or the other, pistol spawns, or weapon spawns
-Decrease the amount of spawns in a given area
-Less mazes and less hallways
All in all your maps actually look just fine, the texturing works together real well and in some cases actually helps bring the outlook of some maps out of a totally negative spotlight. Continue at it as I hope this gets better as time goes on, maybe play some other deathmatch wads to get a better idea of what maps should look and play like.
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Glad you're still working on this, I remember cool MIDI choices as well. Keep up the good work! 
